Just a few minutes ago Ray Ozzie announced in his keynote at the MIX conference in Las Vegas, that the next version of Silverlight will include a fullsize .NET CLR.
This is a mjor step made by Microsoft to extend the .NET development technology on other platforms. Later on Scott Guthri showed how to remote debug a C# application running in a Safari browser on a MacIntosh from Visual Studio running on Windows.
This technology really is exciting because it closes the gap between true platform interoperability while leveraging the powerful Microsoft toolchain. Additionally and fitting good into this strategy, Expression Studio was released. A too that helps to decouples the work process between Designers and developers without making the the reintegration painful. It uses the new application paradigm introduced with the Windows Presentation Foundation coming as part of VISTA and the .NET 3.0 framework.